This invention relates to the art of synthetic plastic resin extruded separable fasteners and a method of making the same, and is more particularly concerned with prefabricating such fasteners at a high rate of production, economically and for subsequent union with desired substrates.
As revealed in the prior art exemplified by U.S. patents, proposals for uniting extruded separable fasteners, sometimes referred to in the trade as zippers, have comprised joining the fastener profile strips to a compatible extruded synthetic plastic film substrate while both of the separately, but simultaneously extruded components are still in a sufficiently plastic state to fuse together, as exemplified in U.S. Pat. Nos. 3,462,332 and 4,259,133.
Another technique, as exemplified in U.S. Pat. Nos. 3,784,432 and 4,279,677, includes joining the freshly extruded profile strips to compatible prefabricated plastic film substrate while the fastener strip is still in a sufficiently thermoplastic state to permit fusing the thermoplastic film which is reheated from a cold state to accelerate the fusion.
A further technique as exemplified in U.S. Pat. No. 3,532,571 includes joining freshly extruded film to compatible prefabricated fastener strips while the film is still in a sufficiently thermoplastic state to permit fusing the fastener strip to the film.
It has, of course, been longtime common practice to join prefabricated fastener strip to prefabricated compatible plastic film by fusion welding, as exemplified in U.S. Pat. No. 3,948,705.
A distinct advantage attributable to prefabricating profile fastener strips and bag making plastic film resides in the fact that because of the relatively larger section modulus of the profile strips as compared to the section modulus of the plastic film, the plastic film when extruded separately can be run at a much greater speeds than the profile fastener strips. Therefore by spooling the prefabricated fastener strips and the prefabricated film is separate rolls, they can be fed simultaneously at desired speed and joined together as by means of adhesive applied in a fluent state between the elements as they are brought convergently together, as exemplified, by U.S. Pat. Nos. 4,101,355; 4,341,575; 4,354,541 and 4,355,494. A distinct advantage of such prefabrication and then adhesive joinder of the profile fastener strips and the substrate is that relatively incompatible materials may be utilized to advantage in the respective elements. For example, a form of plastic material which will lend itself to best advantage for extrusion of the profile strips, and will afford the most advantageous elastic deformation separable coaction of the fastener profiles may be utilized for that purpose, while materials having special characteristics desirable for the end product such as bags may be utilized in the film whether plastic or non-plastic. The composite finished product will then be endowed with all of the preferred characteristic in both the fastener and the substrate.
With all of the advantages inherent in adhesively securing prefabricated elastically deformable separable profile fastener strips to prefabricated film substrate, there is still room for substantial improvement in the adhesive attachment technique. A disadvantage of adhesive attachment as heretofore proposed has been the requirement for extremely accurate control of the fluent adhesive, both as to volume at point of application, temperature gradients during application, tackiness, machine down time, necessarily close attention to the adhesive applicators, avoidance of adhesive spray machine foul-up, and the like. Therefore, onsite adhesive joinder of the profile fastener strips and the substrate has placed a heavy burden on the machine operators to maintain all of the critical parameters necessary for successful results. This has been particularly the case when the adhesive attachment is combined with a form fill operation as described in U.S. Pat. No. 4,355,494, where the advantage of shipping finished film and finished fastener separately and thereby saving space as well as reducing spool change-over because of larger spools, are then lost due to the relatively complex liquid adhesive applying operation.
It has been proposed in published U.K. Patent Application 2,080,412A to provide fastener strips having sidewardly extending attachment webs carrying heat reactivatable adhesive. However, the fastener strips having such attachment webs are more costly to produce than a web-free fastener strip such as disclosed in British Pat. No. 1,587,609. Neither of these British publications has an adequate teaching of how to prefabricate fastener strips with reactivatable adhesive, and in particular such fastener strips without side attachment webs.